High vacuum



June 6, 1939. K. c. D. HICKMAN 2,160,863

HIGH VACUUM Filed June 10, 1937 2 Sheets-Sheet l FIG.1. F1G.2.

Kenneth C.D.Hickman A INVENTOR BY lam/WM ATTORNEYS June 6, K c D HICKMAN HIGH VACUUM Filed June 10, 1937 2 Sheets-Sheet 2 FIG].

He mne (LDHicKman INVENTOR BY M ATTORNEYS Patented June 6, 1939 UNITED STATES HIGH VACUUM- Kenneth C. D. Hickman,

signor, by mesne ass Products, Inc., Rochester,

of Delaware Rochester, N. Y., asignments, to Distillation N. Y., a corporation Application June 10, 1937, Serial No. 141,514 In Great Britain July s, 1936 6 Claims.

This invention pertains to improvements in the production of high vacua and high vacuum pumps.

Pumping apparatus for producing high vacua are known to be decidedly inefficient. The well known Cenco Hyvac pump with a capacity of 100 cc. per second has an efflciency at the fly wheel of about .0038% at a pressure'of .01 mm., or taking the losses of the 1 horse power (200 watts) motor into consideration, an efliciency of, say,

10 .001%. An alternative method of producing high vacua is a condensation pump. A pump of this type consuming 200 watts and having a capacity of 50 liters per second has an efficiency of .5% at .01 mm., and at the moderately high vacuum of 10 mm. the efficiency is only .005%.

This latter type of pump also has the disadvantage that pumping fluids of appreciable vapor pressure must be used.

This invention has for its object to overcome the above diiliculties of high vacuum production. Another object is to provide improved methods and apparatus for producing high vacua. Another object is to provide a high vacuum pump which does not require a liquid or vaporous opcrating fluid and which requires but little energy for operation. A further object is to provide a high vacuum pump which will enable the production of very high vacua and which operates on the principle of adsorption or absorption of gases.

Other objects will appear hereinafter.

These and other objects are accomplished by sorbing the gas from the chamber to be evacuated onto a surface having the ability to sorb gases, discharging the sorbed gases from the sorption surface, removing the discharged gases from the zone of discharge by means of a backing pump and repeating the sorption and discharge steps in order to maintain the desired degree of evacuation.

In the following examples and description, I

, have set forth the preferred methods of carrying out my invention and it is to beunderstood that these are described for the purposes of illustration and not as limitations thereof.

A profound change in the nature of gas takes p'ace as it passes from pressures where it behaves as a continuum to pressures where its properties are those of its individual atoms or molecules.

The change occurs roughly where the mean free path is similar to the dimensions (chiefly diameter) of the parts of the apparatus. At all pressures except at the very lowest, gas is adsorbed to the apparatus walls. At higher pressures where the continuum exists, there are more molecules in the volume than on the walls audit is more economical for pumping purposes to operate on the volume of gas. Where the pressure is so low that the collisions in the gas are less than the collisions with the wall, it is more economical to remove the gases from the walls or surfaces upon 5 which they are absorbed. This result is accomplished by my invention as well as simultaneous removal of gases present in the volume.

My invention can be carried out in numerous types and variations of apparatus. The sorp- 10 'tion surfaces may be in the form of a drum, wheel, band, disc or any surface which can be alternately charged and discharged. The drum, band or disc etc., may be composed of a material which has adsorptive or absorptive properties, or may be 15 constructed of a material which actsas a support for substances having such gas sorptive properties. The discharge of the gases on the high pressure side of a pump can be effected in a number of ways, such as ionization caused by contact 20 with a high tension-electrode, or by heating such as by radiation, by high frequency heating, by electronic bombardment from a glowing filament, etc. In order to simplify the description, the term sorption or sorption surface, will be used 25 as a generic term including both absorption and adsorption.

Various modificationsof my improved pump are shown in the accompanying drawings in which like numbers refer to like parts and in 30 which:

Figs. 1, 2, 3, and 4 are elevations in section of pumps having different types of sorption elements and illustrate various methods for discharging gases from the sorption surface.

Fig. 5 is an elevation in section of a pump having a disc -shaped sorption surface employing electrical resistance heating for discharge of gases.

Fig. 6 is a horizontal section of the apparatus shown in Fig. 5.

Fig. '7 is an elevation in section of a pump having a sorption surface made up of strands of sorbing material and illustrates the position of the sorption element during the sorption of gases.

Fig. 8 is an elevation in section of the same 941- 5 paratus shown in Fig. '7 and shows the position of the sorption element during discharge of the sorbed gases. v

Fig. 9 is an elevation in section of a pump having a stationary sorption surface, and;

Fig. 10 is a vertical section on. line Ill-III of Fig. 9.

Referring to Fig. 1, reference numeral l designates a cylindrical or drum shaped pump casing provided with conduit 2 which connects with the chamber to be evacuated and conduit 3 which connects to the backing pump and, which therefore, represents the low vacuum side of the pump assembly. Reference numeral 4 designates a drum rotatably mounted upon a centrally located shaft 5. About the periphery of drum 4 is mounted a plurality of bristle-like appendages 6 which are constructed of material having sorption properties. for gases. Reference numeral I designates a high voltage electrode so located that it comes into contact with bristles 5 when drum 4 is rotated and in that manner causes heating and electrical discharge of sorbed gases. In operation drum 4 is caused to rotate at any suitable speed depending upon the desired rate of evacuation and the backing pump connected to conduit 3 is put into operation. Gases diffusing from the chamber to be evacuatedinto conduit 2 are sorbed upon the surfaces of bristles 6 and are carried from the point of sorption to the high pressure side of the pump and are discharged by the electrode 1 and removed from the system through conduit 3.

Referring to Fig. 2, reference numerals I, 2, and 3 designate a pump housing and conduits arranged in the same manner as described in connection with Fig. 1. A rigid circular band I5 is centrally located within the housing I and is rotatably mounted upon rollers l6, one of which is driven. Band I5 is constructed of a metal having sorptive propertiessuch as tungsten or molybdenum, or its surface is coated with a material, such as silica gel, alumina, active carbon or other material having such an action. Numeral I I designates a discharge device which comprises a metal coil looped about the band l5 and which is connected to a high frequency cur-g rent by connecting wires l8. During the operation, gas diffusing from the chamber to be evacuated is sorbed onto the surface of. rotating band 15 and is conveyed to the high pressure side of the pump where the band is heated by device I! and the gases caused to be discharged. Gases are removed from conduit 3 by a backing pump connected thereto.

Referring to Fig. 3, reference numeral 25 designates a pump housing provided with intake and withdrawal conduits 2 and 3 respectively. Reference numerals 26 and 21 designate drum shaped members rotatably mounted on shafts 28 and 29 in such manner that the-surfaces are in light contact or in close proximity to each other. shafts 28 and 29 respectively and are connected together by lead wire 32. Numeral 33 designates a filament extending in the same direction as the surface of the drums 26 and 21 and which is connected to lead wires 34 and 35. In operation,

drums 26 and 21 are caused to rotate in the ,di-

rection indicated and conduit 3 is connected to a backing pump. Wires 34 and are connected to a low voltage supply suflicient to heat filament 33 to incandescence. Lead wires 32 and 35 are connected to a high voltage supply. Since a relatively high vacuum exists during all stages of operation, the filament 33 is not damaged. Due to the high difference in potential between drums 26 and 21 and filament 33 electronic bombardment of the surfaces of the drums near the filament takes place, which results in heating and discharge of gases sorbed thereon. Discharged gases are removed thro gh conduit 3 by the backing pump.

In Fig. 4, reference numeral 50 designates a conduit of square or rectangular cross section in Brushes 30 and 3! make contact with plate ")6 provided which is mounted an endless band 5| supported by rolls 52 and 53 which are mounted upon shafts 54 and 55. One or both of these shafts are driven in order to cause band 5| to travel in a circuitous path around the drums 52 and 53. Numeral 56 designates a heated filament or glow lamp and 51 a reflector. During operation conduit 50 is connected at the leftto the receptacle to be evacuated and'at the right to a backing pump which is put into operation. Filament 56 is heated and band 5| is caused to rotate. Gases from the receptacle are sorbed on the surface of. band 5| as it passes over roll 52 and are discharged by the radiant heat from filament 56 and reflector 51 as it passes over roll 53. Discharged gases are removed by the backing pump.

Referring to Figs. 5 and 6 numeral 10 designates a shallow or squat, closed cylinder which serves as the pump casing. Intake and withdrawal conduits 2 and 3 are connected. at diametrically opposite sides of casing 10. Numeral H designates a disc which is rotatably mounted upon shaft 12 which is driven by gear 13. The disc is preferably constructed of metal having gas sorptive properties, and a surface which has such properties as well as the ability to conduct electricity. Numerals 14 and 15 designate electrodes or brushes which contact with shaft 12 and the surface -of disc II respectively. During operation disc H is caused to rotate, by energy applied to gear 13. A low voltage high amperage current is applied to brushes 14 and 15 which causes the surface of the disc near the brush 75 to become heated. Gases from the receptacle being evacuated are sorbed on the surface of the disc exposed at conduit 2 and are caused to be discharged at the withdrawal conduit 3 by that area.

In Figs. 7 and 8 numerals 2 and 3 designate the high and-low vacuum sides of. the pump. Numeral 90 designates a shield which has the form of a half-sphere and is rotatably mounted at approximately the center of curvature upon shaft 9| by means of supports 92. Numeral 93 designates a plurality of strands'of electrical conducting material which also has the ability to sorb gases and which is preferably of large surface area. These strands are connected to a low voltage source of current in a conventional manner, so that current can be passed there through in order to heat them when desired.

must at least have the heat generated in After the backing pump has been put into operthrough conduit 3. by the backing pump and the element 90 returns to the position shown in Fig. 7 for the s'orption of additional gases.

In Figs. 9 and 10 is illustrated a pump having a stationary sorption surface and a rotating discharge device. Referring to the figures numeral I05 designates a corrugated, cylindrical pump casing having the high and low vacuum ends 2 and 3 respectively. An approximately elliptical with horizontal projections I01 and I08 is rotatably mounted upon shaft I09 which is in turn supported in the center of the casing by spider supports-H0 and Ill. Baflies H2 and 3 are fixed to plate I06 at a point corresponding to the center of corrugations I and H5 as illustrated. Numeral H6 designates a lagged electrical heating plate which is corrugated in the same manneras casing I05 and which covers only a portionof the circumference of the casing. The plate is mounted upon rings H1 and H8 so that it is in close proximity to the surface of the casing-I05, but slightly out of contact therewith. Rings III and H8 are mounted in and supported by rolls H9 one or more of which are driven. An electromagnet I20 is mounted upon the heating pad at a position opposite projection I01 which is constructed oi magnetic material. Casing I05 is rigidly supported in the position shown so that when pulleys H9 are actuated the heating plate H6 and magnet I20 revolve about the casing without coming into contact with its surface.

During operation the high vacuum end 2 of the pump is connected to the receptacle, to be evacuated and the low vacuum end 3 to the backing pump. The backing pump is put into operation and gas is sucked from the receptacle into the casing and passes through the openings between casing I05 and plates H2 and H3 and projection I08 and thence into the backing pump. Plate H6 is then heated and driving pulley H9 actuated. Due to the attraction between magnet I20 and projection I01, plate I05 and baffles H2 and H3 rotate and are always in the same relative positionto heating plate H5 as illustrated in Fig. 9. Since the inside surface of easing I05 is constructed of material having good sorptive' properties, gases diffusing into it be come sorbed thereon. With the heating plate I I6 and plate I in the position shown, the top part of easing I'is heated and sorbed gases are driven 01f. The discharged gases are prevented from returning to the high vacuum side by plate I05 and they are therefore removed from the-space between plate I06 and the top wall of the casing I05 by the backing pump. At

1 the same time gases diffusing into the high vaccasing uum side are absorbed on the bottom surface of I05. As the heating plate and plate. I06 rotate they will eventually reach the bottom of the casing where discharge of gases takes place while gases will be sorbed at the top. While the above description involves only the action which takes place at the top and bottom of the casingit will be apparent that regardless of the position of the heating plate H6, gases will be discharged in its vicinity, while at the opposite side of the casing I05 sorption of gases will be taking place. Therefore each rotation of the moving elements will result in a cycle of sorption and discharge of gas on each unit area of the inside of casing I05.

It will be apparent that many widely different types of apparatus other than those illustrated can be employed without departing from the spirit or scope of my invention. For instance the main casing of the apparatus illustrated in Figs. 9 and 10 may be a smooth cylinder instead of corrugated. The corrugated surface is preferable however since it decreases the amount of diffusion back into the high vacuum end of the pump. Although I prefer to employ cylindrical, endless band or disc shaped sorption surfaces, other shapes and kinds of surfaces can be used. Since the pump performs best when it forms part of the wall of the chamber to be evacuated it is best to have the sorption surface near the chamber or form a part of its wall. However the pump removes gases from the space itself as well to the unaided eye.

as from the walls so that substantially greater distances can be used without substantial loss in emclency. Rotation of the pump elements can be accomplished by a number of methods other than by an external shaft provided witha packing gland. For instance a telechron motor connected to the shaft to be rotated can be placed inside the pump casing, or an induction motor with a field outside the casing may be used. Another method similar to that of Fig. 9 is to employ an external rotating magnet with an armature inside the casing. Various methods for discharging the gases from the sorption surface can be employed and it will be apparent that those illustrated with one particular design of pump can be used with pumps of the other types illustrated. Several sorption pumps can of course be used in series.

Although smooth sorption surfaces are suitable, I prefer to employ those having rough surfaces. By a rough surface is meant one which presents large differences in surface elevation as compared to the size of gas molecules. Such surfaces may appear to be substantially smooth All polished surfaces contain molecular crevices, while rough: surfaces have relatively enormous ravines lined with mo lecular crevices. Since practically no surface is smooth in this sense it is more a matter of expediency as to which should be used.

A large variety of materials other than those mentioned can be employed as construction materials for the sorption surfaces. The material used should not of. course be one which has a higher vapor pressure than the degree of vacuum which is to be obtained. Materials such as mica, glass, metal salts, metals such as copper, iron, nickel, platinum, platinum black, palladium, cellulose and its derivatives such as cellulose acetate and other esters and ethers, resin plastics, etc. have sorptive employed for this purpose. The use. of mate rials having an extremely large surface area such as activated carbon, silica gel, alumina, silicates such as zeolites etc. are advantageous and can be formed or coated upon the pump surfaces in anydesired manner. When the sorbing material is in the form of fabric or bristles it can be semi-conducting so that the high tension discharge can leak through them down to the boss onto which they are fastened. This can be accomplished by impregnation with salts or other conducting or semi-conducting material. Cellulose derivative fibers, hogs bristles, felt, vegetable flber, wood, etc., are examples of suitable construction materials of this nature.

In cases where a particular kind of gas is to be pumped, the; sorption surface may be constructed of, or-contain. a material which has a particular ailini-ty for the gas. For instance, if a mercury condensation pump is to be used as a backing pump for the sorption pump it would be advantageous to use a sorption surface having an aflinity for mercury vapor as well as for gases. would be suitable in such a situation. Mercury molecules would amalgamate with the gold surface and on being heated to red heat would be action and may be A sorption pump having gold surfaces.

discharged into the backing pump. In this way that it is necessary to employ sorption pumps with a backing pump, since they will not operate under normal or slightly reduced pressures. It is desirable that a backing pump capable of giving a low pressure he used. The sorption pump can operate at pressures as high as 1 mm. when sorption surfaces are used which are coated with a material having special ailinity for selected molecular species. Backing pressures of about .1 mm. and below increase the pumping speed, the most useful range being below about .01 mm. such as .001 mm. and downward. Since the sorption pumps operate best at pressures where the resistance to gas flow is relatively great, the clearances between the sorption surface and the pump casing need not be close. It will, however, vary with the backing pressure employed. A clearance of about 1 mm. is required with an absorption pump designed to operate at about .1 mm. and downward, while a larger sized pump operating at 10- mm. on large volumes of gas can have a clearance of 1 cm. or more. The clearance should be large enough to allow passage of gas during the preliminary exhaustion at higher pressures and small enough so that molecules cannot pass by without suffering many collisions with the sorption surface.

The speed of rotation of the sorptionsurface depends upon the size of the pump, the speed of evacuation desired and the pressure under which it is operating. Obviously the rate of evacuation is proportional to the rate of rotation of the pump clement. Speeds of one to ten thousand revolutions per minute are suitable for all usual purposes although slower or higher speeds may be desirable with certain types of pump construction or under particular conditions.

The sorption pumps disclosed enable a rapid and eflicient removal of gases and are particularly advantageous whenit is desired to produce vacua of a very high degree. Lower pressures can be obtained than with. condensation pumps due to the fact that there is no volatilizable material employed and the problem of vapor pressure of pumping fluids is entirely eliminated. Since the rotating members of the pump-can be delicately mounted and are not of great weight, the energy required to rotate them even athigh speeds is very low, being only a fraction of that required to produce a vapor stream of the liquid pumping fluid in a condensation pump.

WhatIclaim is: i 4

1. The process of producing high vacua which comprises sorb n Ems from the zone to be evacuated upon a surface Having the ability to sorb gases, moving the charged surface to a point where a pressure of less than about .1 mm. is maintained, discharging the sorped gases in the neighborhood of this point by heating or otherwise treating said surface and returning the surface for sorption of additional gas.

2. The process of claim 1 in which the discharge of gases from the sorption surface is caused by high frequency heating.

3. The process of producing a high vacuum which comprises producing a relatively high vacuum in the system to be evacuated by conventional pumping methods as by the operation of a backing pump, causing a surface having the property of adsorbing gases to move from the chamber to be evacuated to a point communicating with the intake of the conventional backing pump, sorbing gases on the adsorption surfaceat a point communicating with the chamber to be evacuated and then treating the adsorption surface to cause the gases to be discharged in the vicinity of the backing pump intake.

4. Pumping apparatus for producing a high vacuum in a closed receptacle which comprises in combination, a backing pump for maintaining the receptacle at a pressure of .1 mm. or less, an enclosed sorption surface, a conduit communicating with the receptacle which is to be evacuated and with the sorption surface, means for repeatedly exposing the sorption surface from a position communicating with the receptacle to be evacuated to a position in open communication with the intake of the backing pump, heating means for discharging gases from the sorption surface at the position adjacent the intake of the backing pump, means for preventing discharged gases from passing back into the receptacle, and a conduit through which discharged gases can be removed by the backing pump from the place at which they were discharged.

5. Pumping apparatus for producing a high vacuum in a closed receptacle which comprises in combination, a backing pump for maintaining the receptacle at a pressure of .1 mm. or less, an enclosed sorption surface, a conduit communicating with the receptacle which is to be evacuated and with the sorption surface, a second conduit communicating withthe sorption surface and the intake of the backing pump, means for discharging gas from the sorption surface at a position communicating with the intake of the backing pump, and means for moving the sorption surface from a position communicating with the receptacle to be evacuated to a position in communication with the intake of the backing pump.

6. Pumping apparatus for producing a high vacuum in a clased receptacle which comprises in combination a backing pump -for maintaining the receptacle at a relatively low pressure, an enclosed endless sorption surface, a conduit com municating with the receptacle to be evacuated and with one side of the sorption surface, a second conduit communicating with the approximately opposite side of the sorption surface, heating means for discharging gases from the sorption surface and with the intake of the backing pump .at a point communicating with the second conduit and means for causing the endless sorption surface to continuously pass between the two positions at which it communicates with these two conduits.

KENNETH C. D. HICKMAN. 

